This invention relates to a magnetographic apparatus.
In an apparatus utilized for magnetography or zerography of the conventional type, a sequence of processes for forming a latent image, for developing the latent image, for transferring the developed image and for erasing the latent image is conducted for the production of one copy. Such conventional type magnetographic apparatus are disclosed in, for example, U.S. Pat. Nos. 4,005,439 and 4,030,105.
However, frequent repetitions of the entire sequence of processes for forming a latent image, for developing the latent image, for transferring the developed image and for erasing the latent image for producing each copy are too complicated and too uneconomical. Furthermore, such repetitions accelerate the deterioration of the quality of the magnetic recording drum.
The inventors of the present invention conceived the idea of producing copies by repetitively using the same latent image on the drum, and made investigations into the conditions required for the apparatus utilized for producing a large number of good quality copies which repeatedly uses the same latent image on the drum.
The conditions which were investigated are as follows:
A. Access of the recording head to the recording drum.
B. Control of the magnetic force of the developing roller situated in the magnetic toner supplying portion adjacent to the surface of the recording drum.
C. Application of the electrostatic bias to the transferring portion where the developed image is transferred from the recording drum to the copy paper.
D. Utilization of the pressure fixing method in the fixing portion.
E. Selection of the optimum speed of the recording drum for the latent image formation and for the repeated copy production, respectively.
F. Selection of the material and the strength of the recording drum.
G. Selection of the material of the magnetic toner and the mixing ratio between the toner and the carrier included in the magnetic toner.
H. Selection of the method for cleaning the recording drum.